network: Use "prefix length" for IPv6

Previously the term "Netmask" was used incorrectly for the IPv6
prefix length. The name is now corrected and additionally only an
integer is allowed as the prefix length.

Change-Id: I18e7829e7c9e4b265822d02aa86c34f8fda41519
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=981168
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>
network: Don't remove bonding module on cleanup

Previously the bonding module got unloaded to remove all bonds on the
system, but this conflicted with other parts of Node, namely vdsm.
Therefor now the bonds are removed by bringing down each device on it's
own.

Change-Id: Ia2eada10beeb981ecf6b4dbe1b51d2c38f8daea7
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=995155
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>